Electric lamp and discharge devices – With gas or vapor – With particular gas or vapor
Patent
1995-09-25
1997-06-03
Horabik, Michael
Electric lamp and discharge devices
With gas or vapor
With particular gas or vapor
H01J 6120
Patent
active
056357966
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a high-pressure metal-halide discharge lamp with a mean arc power between 60 and 140 W/mm arc length, for fitting in optical systems, as generically defined by the preamble to claim 1. High-pressure metal-halide discharge lamps of this type are used particularly in projection systems (slide projectors, overhead projectors, amateur and professional movie projectors) and glass fiber lighting systems (endoscopy, microscopy, effect lighting for film and television), where light with color temperatures between 4000 and 7000 K and good to very good color reproduction in all color temperature ranges are needed. They are distinguished by a very short arc light (a few millimeters) and maximum light densities (on average, several tens of kcd/cm.sup.2), which predestines them for installation in reflectors or other optical imaging systems.
European Patent Disclosure EP 0 193 086 and German Patent Disclosure DE-A 4 040 858 disclose high-pressure metal-halide discharge lamps with short arcs and correspondingly high light densities, which produce light with a spectral composition similar to daylight. However, their disadvantage is that these lamps have average service lives of only a few hundred hours.
The object of the invention is to create a high-pressure metal-halide discharge lamp that has an average service life of at least 1000 hours of operation, has a very short arc with very high light density, and has a color temperature between 4000 and 7000 K = with very good color reproduction--and that attains this goal with the fewest possible elements in its filling.
This object is attained by the characteristics of the body of claim 1. Other advantageous characteristics are recited in the dependent claims.
The high-pressure metal-halide discharge lamp according to the invention is operated at specific arc powers between 60 and 140 W/mm of arc length and at comparably low wall loads of between 40 and 85 W per cm.sup.2 of wall area. With conventional fillings, at wall loads below or above approximately 60 W/cm.sup.2, bulb blackening or devitrification occurs within a short time, and the value for these limits can vary depending on the cooling. As a result, the useful light flux drops, and the lamp life is shortened.
To the filling of the lamp according to the invention--which comprises mercury, at least one noble gas and at least one halogen and cesium--tantalum and dysprosium are added, preferably in a ratio by weight of between 0.3 and 1.5; the total quantity of these two important additives to the filling is advantageously between 0.2 and 1.5 mg/cm.sup.3. Tantalum maintains the halogen cycle process even at relatively low wall loads and thus largely prevents blackening and devitrification of the bulb, so that a long average service life can be attained. Tantalum also contributes to the continuum proportion in the optical spectrum. Dysprosium, with its multi-line spectrum, assures a high radiation flux in the visible range of the optical spectrum. By means of the addition of tantalum and dysprosium according to the invention, the tendency to devitrification and blackening of the bulb is accordingly minimized--that is, the mean service life is correspondingly prolonged--and the light flux and the color reproduction are optimized.
If the color temperature is to be lowered and/or particularly good color reproduction is to be attained, then optionally lithium can be added in addition, in a proportion up to 0.2 mg/cm.sup.3 of the vessel volume; this increases the red proportion in the radiation, which can be advantageous particularly when the lamp is used in a dichroitic cold-light reflector, which raises the color temperature of the reflected radiation somewhat compared with the total radiation of the discharge. Moreover, lithium is an atomic line radiator, which radiates preferably in the hot arc core and is therefore projected especially efficiently by suitably focusing special reflectors that project only the inner arc core.
For arc stabilization, the discharge vessel can contain cesium in a pro
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Day Michael
Horabik Michael
Patent-Treuhand-Gesellschaft fur elektrische Gluhlampen mbH
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